Bottled water dispensers are frequently used in manufacturing plants and chemical factories to provide a supply of water convenient to the area where the employees are working. In many work areas, the air is contaminated with dust from the materials being worked upon. In chemical plants, the air is often contaminated by solvents and dust from solid materials being used in chemical processes and from finished product. The bottled water dispenser stands surrounded by this environment. When an employee takes a drink from the bottled water dispenser, the water pours from a reservoir into the cup or container held in the hand of the employee. As we are all familiar, air must enter the water supply bottle to relieve the partial vacuum in order for the water to empty from the bottle. The air frequently bubbles in an erupting stream of large and small bubbles which carry with them all of the contaminants in the ambient air surrounding a water cooler. As successive employees draw water from the dispenser, the air continues to bubble into the supply bottle further contaminating the water as well as the water in the reservoir in the water dispenser. In order to avoid this health hazard, it would be desirable if the water in the water supply bottle could be protected from contamination as it empties and is displaced by the necessary air. Also, it would be convenient if this could be done using conventional water bottles which are not modified in any way.